package Cwd;
require 5.000;
require Exporter;
require Config;

# Use osname for portability switches (doubled to cheaply avoid -w warning)
my $osname = $Config::Config{'osname'} || $Config::Config{'osname'};


=head1 NAME

getcwd - get pathname of current working directory

=head1 SYNOPSIS

    use Cwd;
    $dir = cwd;

    use Cwd;
    $dir = getcwd;

    use Cwd;
    $dir = fastgetcwd;

    use Cwd 'chdir';
    chdir "/tmp";
    print $ENV{'PWD'};

=head1 DESCRIPTION

The getcwd() function re-implements the getcwd(3) (or getwd(3)) functions
in Perl.

The fastcwd() function looks the same as getcwd(), but runs faster.
It's also more dangerous because you might conceivably chdir() out of a
directory that you can't chdir() back into.

The cwd() function looks the same as getcwd and fastgetcwd but is
implemented using the most natural and safe form for the current
architecture. For most systems it is identical to `pwd` (but without
the trailing line terminator). It is recommended that cwd (or another
*cwd() function) is used in I<all> code to ensure portability.

If you ask to override your chdir() built-in function, then your PWD
environment variable will be kept up to date.  (See
L<perlsub/Overriding builtin functions>.) Note that it will only be
kept up to date it all packages which use chdir import it from Cwd.

=cut

@ISA = qw(Exporter);
@EXPORT = qw(cwd getcwd fastcwd fastgetcwd);
@EXPORT_OK = qw(chdir);

# use strict;

sub _backtick_pwd {  # The 'natural and safe form' for UNIX (pwd may be setuid root)
    my $cwd;
    chop($cwd = `pwd`);
    $cwd;
} 

# Since some ports may predefine cwd internally (e.g., NT)
# we take care not to override an existing definition for cwd().

*cwd = \&_backtick_pwd unless defined &cwd;


# This used to be written in perl; now we use a builtin function.
# (The perl version would stat files in each parent directory, which is
# slow and possibly prohibitive in a global distributed filesystem.)
#
# Usage: $cwd = getcwd();

sub getcwd {
    getcwd;
}

# This was a faster version of getcwd.  Now we use the builtin
# function.

sub fastcwd {
    getcwd;
}

# keeps track of current working directory in PWD environment var
#
# $RCSfile: Cwd.pm,v $$Revision: 1.3 $$Date: 1996/06/03 02:45:01 $
#
# $Log: Cwd.pm,v $
# Revision 1.3  1996/06/03 02:45:01  ghudson
# Merge in perl 5.002
#
# Revision 1.2  1995/09/29 19:20:32  ghudson
# Use builtin getcwd function for getcwd() and fastcwd().
#
# Revision 1.1  1995/09/29  19:06:09  ghudson
# Initial revision
#
#
# Usage:
#	use Cwd 'chdir';
#	chdir $newdir;

my $chdir_init = 0;

sub chdir_init {
    if ($ENV{'PWD'} and $osname ne 'os2') {
	my($dd,$di) = stat('.');
	my($pd,$pi) = stat($ENV{'PWD'});
	if (!defined $dd or !defined $pd or $di != $pi or $dd != $pd) {
	    $ENV{'PWD'} = cwd();
	}
    }
    else {
	$ENV{'PWD'} = cwd();
    }
    # Strip an automounter prefix (where /tmp_mnt/foo/bar == /foo/bar)
    if ($ENV{'PWD'} =~ m|(/[^/]+(/[^/]+/[^/]+))(.*)|) {
	my($pd,$pi) = stat($2);
	my($dd,$di) = stat($1);
	if (defined $pd and defined $dd and $di == $pi and $dd == $pd) {
	    $ENV{'PWD'}="$2$3";
	}
    }
    $chdir_init = 1;
}

sub chdir {
    my $newdir = shift || '';	# allow for no arg (chdir to HOME dir)
    $newdir =~ s|///*|/|g;
    chdir_init() unless $chdir_init;
    return 0 unless CORE::chdir $newdir;
    if ($osname eq 'VMS') { return $ENV{'PWD'} = $ENV{'DEFAULT'} }

    if ($newdir =~ m#^/#) {
	$ENV{'PWD'} = $newdir;
    } else {
	my @curdir = split(m#/#,$ENV{'PWD'});
	@curdir = ('') unless @curdir;
	my $component;
	foreach $component (split(m#/#, $newdir)) {
	    next if $component eq '.';
	    pop(@curdir),next if $component eq '..';
	    push(@curdir,$component);
	}
	$ENV{'PWD'} = join('/',@curdir) || '/';
    }
    1;
}


# --- PORTING SECTION ---

# VMS: $ENV{'DEFAULT'} points to default directory at all times
# 08-Dec-1994  Charles Bailey  bailey@genetics.upenn.edu
# Note: Use of Cwd::getcwd() or Cwd::chdir() (but not Cwd::fastcwd())
#   causes the logical name PWD to be defined in the process 
#   logical name table as the default device and directory 
#   seen by Perl. This may not be the same as the default device 
#   and directory seen by DCL after Perl exits, since the effects
#   the CRTL chdir() function persist only until Perl exits.
# This does not apply to other systems (where only chdir() sets PWD).

sub _vms_cwd {
    return $ENV{'DEFAULT'}
}
sub _vms_pwd {
    return $ENV{'PWD'} = $ENV{'DEFAULT'}
}
sub _os2_cwd {
    $ENV{'PWD'} = `cmd /c cd`;
    chop $ENV{'PWD'};
    $ENV{'PWD'} =~ s:\\:/:g ;
    return $ENV{'PWD'};
}

if ($osname eq 'VMS') {

    *cwd        = \&_vms_pwd;
    *getcwd     = \&_vms_pwd;
    *fastcwd    = \&_vms_cwd;
    *fastgetcwd = \&_vms_cwd;
}
elsif ($osname eq 'NT') {

    *getcwd     = \&cwd;
    *fastgetcwd = \&cwd;
}
elsif ($osname eq 'os2') {
    *cwd     = \&_os2_cwd;
    *getcwd     = \&_os2_cwd;
    *fastgetcwd = \&_os2_cwd;
    *fastcwd = \&_os2_cwd;
}

# package main; eval join('',<DATA>) || die $@;	# quick test

1;

__END__
BEGIN { import Cwd qw(:DEFAULT chdir); }
print join("\n", cwd, getcwd, fastcwd, "");
chdir('..');
print join("\n", cwd, getcwd, fastcwd, "");
print "$ENV{PWD}\n";